Method of coating printed surfaces and article formed thereby



Patented Dec. 26, 1939 BEST AVAILABLE COPY METHOD OF COATING PRINTED SURFACES AND ARTICLE FORMED THERE'BY Roy E. Coleman, Meriden, Conn, assignor to The Zein Corporation of America, a corporation of Delaware No Drawing.

Application November 22, 1937,

Serial No. 175,888 10 Claims. (01.91-67.11)

This invention relates to methods of coating printed surfaces and more particularly to meth-' ods of coating printed labels with protective varnishes made from zein or other prolamins and to the article produced thereby. The invention set forth herein is related to the invention described in my copending application Serial No. 158,215, filed August 9, 1937.

In the following description of the method embodying my invention I will refer to the preparation of substantially non-aqueous varnish compositions made from zein derived from corn, but it is to be understood that my invention is also applicable to the preparation of varnish compositions made from the other prolamins such as, for example, gliadin from wheat, hordein from barley, kafirin from kafir and the prolamins from other cereal grains. The abovementioned prolamins are at present derived by extraction with an aqueous alcohol solution in which the added water varies generally from about 15 to about 40% of the solvent mixture. The material utilized in preparing the varnishes used in accordance with my invention is the dried extract which may be completely dried or the commercial product which contains a small percentage of moisture.

In carrying out my invention, a printed surface such as, for example, a label, carton, advertising card, playing card, magazine cover and the like, printed with, for example, an oleaginous base type of ink, is covered with a thin, flexible, transparent film of a zein varnish, suitably by machine coating, dipping, spraying or over-printing process or by other suitable coating process. The varnish film formed of such varnish dries in a relatively short time, in the order of about 2 to minutesat room temperature, owing to the fact that zein solutions give up their solvent with extraordinary readiness; and they form a hard, transparent film having a high gloss which appears to accentuate and intensify the underlying printed matter. This drying time may be materially hastened by the application of heat and is, of course, influenced by the, characteristics of the solvents utilized in eflecting solution of the zein, by modifying agents, by the thickness of the film, etc.

In general, the usually dry zein varnish films are compatible with glue or similar water-soluble adhesive materials. Hence the dried zein varnish films present a surface that may be coated with glue which, on hardening, is capable of forming a strong, adherent layer on the varnish films. This characteristic of the films formed in accordance with the method embodying my invention renders the method especially suitable for label printing, since the necessity for the provision of an unvarnished area to which glue may be applied, as in the prior art, is eliminated.

, In accordance with the prior art practice, a localized unprinted and unvarnished area on a labelis necessary so that glue may be applied and adhere thereto for the purpose of securing the label around a can or the like, since glue is not compatible with and does not adhere to the usual oleaginous materials comprising the ink base or the usual varnish coatings. In practice, the labels are first printed with the desired design and a localized, unprinted area is provided to which the glue may be applied. After drying, the printed labels are coated with a, protective varnish over all but the unprinted localized area by means of a printing machine, as an overprint varnish. This practice. is objectionable from the standpoint of the time required to overprint in registry with the printed area to be protected by the varnish, the difliculty of preventing oiT-setting, and the drying time and these requirements render the process costly.

In accordance with my present invention, these objections are overcome by the provision of a zein film as the protective coating, which may be applied as an all-over coating by any of the conventional coating processes. The zein protective coating readily adheresto any printed surface, even when an oleaginous base type of ink has been used for the printing, and dries rapidly. The glue may then be applied to the desired localized area of the zein film for securing the label to the desired object and ondrying, the glue forms a perfect bond with the zein surface. vAccordingly, by operating in accordance with my invention a substantial saving of time is efiected andthe objections to the overprinting and varnishing as in the prior art are obviated.

The printed labels, magazine covers and the like, when coated with the zein varnish in accordance with my method, appear to resist curling or crinkling when in contact with water or aqueous mediums. They are substantially as flexible as the untreated labels, magazine covers and the like and, in some instances, more so; and have a marked resistance to oleaginous materials.

The varnish compositions used in accordance with the present invention are substantially nonaqueous solutions of zein containing preferably from 0 to 5% of added water. while the inclusion oflarselffipercentages of water is not precluded, I have found that the fleld of applicabilbe understood that other varnish compositionsin other proportions may be used in accordance with my invention all as hereinbefore set forth.

In the examples, the term parts" indicates parts by weight.

Example 1 10 parts of zein are mixed with 30 parts of propylene glycol. On stirring the mixture at room temperature the zein mixes readily with the propylene glycol but does not dissolve. n heating to about 160 to 190 F. a perfectly clear, transparent, bright, stable zein varnish is obtained in about 8 to 15 minutes. This varnish is coated onto a printed surface in a conventional coating machine and the coating dries in about 30 to 60 minutes to form a transparent, strongly adherent film which is both hard and flexible and has a very high gloss. renders the printed surface moisture and oil resistant.

Example 2 v parts of zein are mixed with 40 parts of diacetone alcohol (acetone free) and heated in the order of about 165 to 190 F. to form a colloidal, slightly cloudy zein varnish composition. This varnish, on cooling and standing becomes quite viscous but turns transparent and remains stable.

This varnish is now applied onto a printed labeleither on a coating machine, or by overprinting and in about to minutes the coating dries to a transparent, flexible, strongly adherent fllm having a high gloss. The film renders the label substantially moisture and oil resistant and accentuates the printed matter appearing thereon.

Emmple 3 10 parts of zein are mixed with parts of a solvent mixture containing 10% of ethylene glycol monomethyl ether and of alcohol. On stirring and with the application of heat in the order of about 90 to F., a stable zein varnish is obtained in about 8 to 12 minutes.

This composition is now thinned, as by the addition of the solvent mixture, until the varnish has a viscosity suitable for use in a spray gun. The thinned varnish is then sprayed onto a label or printed magazine cover and in about 5 minutes the coating dries to a hard, flexible, transparent fllm having a very high gloss. The zein varnish flhn renders the label or magazine cover moistureand oil resistant, and both accentuates and in surface}? I Example4 10 parts of zeinv are mixed with 40 parts of diacetone alcohol (acetone free) and 6 parts of lauric acid. In practice, the zein is mixed with the diacetonealcohol and heated to about 165 to 190 F., for about 8 to 12 minutes to eifect solu- The zein varnish the printed matter on the coatedtion. The solution; is then cooled toy ab'out to F., and thelauric acid is then added to form a stable zein varnish.

The varnish is applied to a printed label as by over-printing and in about 10 to 15 minutes a clear, transparent, hard and glossy fllm is formed which imparts both moisture and oil resistance to the label. Hr

The films produced on. the printed surfaces as above described have no after-tack, will not resoften on heating and are, for all practical purposes, scratch-proof. I zein fllm to fllm or film to paperbonds may be effected with any of the convention'al water-soluble glues or adhesives.

In carrying out the process according to my "invention a decided advantage inures to the operator since, the zein varnishes used in accordance with my invention have the unusual property of being able to dissolve in themselves even after having remained and dried on the coating rolls or other coating machinery. By virtue of this fact the coating machinery parts need not be cleaned of coating materials immediately after the end of a run or after a break-down as is now required in the prior art processes. s

The characteristics of the varnish compositions used in accordance with my invention and hence of the ultimate protective films can be altered at will and as desired by the inclusion in the varnish composition of diluents, modifiers, plasticizers and the like as set forth in my aboveidentified copending application. The characteristics, such as spread and flow, of these varnishes may also be modified by the addition of a fatty acidsuch as, for example, oleic, linseed, hemp seed, lauric and like fatty acids and by the in clusion of cetyl, lauryl, myristyl and like fatty alcohols having 8 or more carbon atoms in the chain. If desired, compatible natural and synthetic resins such as for example, rosin, sandarac, copal, phenol-aldehyde, urea-aldehyde, glycerinephthalic anhydrid, vinyl and like resins, or compatible cellulose derivatives such as, for example, high and low viscosity nitrocellulose, cellulose acetate, ethyl cellulose and like cellulose derivatives may be incorporated with these zein varnishes in varying proportions to meet the desired needs. I

In the claims when I use the expression "substantially non-aqueous I refer to varnish compositions made from zein or the other prolamins wherein the added water is preferably 5% or less. When I use the expression stable I mean varnish compositions which do not separate on standing or even when cooled to temperatures of 50 to 70 F. and somewhat below. The stable substantially non-aqueous varnishes are capable of drying to a clear, transparent flexible, and hard fllm.

I claim:

1. The method of protecting a printed surface which comprises coating the printed surface with a zein varnish capable of drying to a hard, transparent film, said varnish containing not in excess of 5% of water.

2. The method of applying a protective coating layer to a printed label which comprises coating the printed surface of the label'with a zein varnish capable of drying to a hard, flexible, transparent fllm, said varnish containing not in excess of 5% of water.

3. The method of applying a protective coating layer to a printed label which comprises coating the printed surface of the label with a varnish comprising zein and propylene glycol capable of film, said varnish containing not in excess of 5% of water.

4. The method of applying a protective coating layer to a printed label which comprises coating the printed surface of the label with a varnish comprising zein and diacetone alcohol capable of drying to a hard, glossy, flexible, transparent film, said varnish containing not in excess of 5% of water.

5. The method of applying a protective coating layer to a printed label which comprises coatin the printed surface of the label with a varnish comprising zein, diacetone alcohol and lauric acid capable of drying to a hard, glossy, flexible, transparent film, said varnish containing not in excess of 5% of water.

6. The method of applying a protective coating layer to a printed label which comprises coating the printed surface of the label-with a varnish comprising zein, ethylene glycol monomethyl ether and 95% alcohol capable of drying to a hard, glossy, flexible transparent film, said var-' printed matter, said coating layer being adapted to receive a coating of glue capable of drying to a hard, adherent layer on said zein coating layer, said layer being deposited from a liquid zein coating composition containing not in excess of 5% of water.

8. A printed label carrying a hard, flexible, glossy, transparent prolamin coating layer over the printed matter, said layer being deposited from a liquid prolamin coating composition containing not in excess of 5% of water.

9. A label printed with an oleaginous base type of ink carrying a hard, flexible, glossy, transparent zein coating layer over the printed matter and a coating of glue along a localized area of the zein film, said layer being-deposited from a liquid zein coating composition containing not. in excess of 5% of water.

10. The method of printing and coating a label comprising, printing a label with an oleaglnous base type of ink, coating the printed surface with a liquid zein composition containing not in excess of 5% of water and which is capable of adhering to the printed surface and coating a localized area of the zein surface with glue.

ROY E. COLEMAN. 

